In a typical hard disk drive (HDD) data storage device, servo sectors on the disk are used to provide position information about the location of a magnetic head over a disk surface. A common approach for writing such servo information on the disk is referred to as spiral-based self servo writing, or spiral-based SSW. According to this approach, spiral-shaped positioning signals (or “servo spirals”) are written on the disk surface prior to the SSW process. During the SSW process, each magnetic head of the HDD is positioned relative to a disk surface based on the servo spirals, so that the final servo information on each disk surface can be written by the disk drive heads.
For an error-free and robust SSW process, the servo spirals used should be precisely written on the disk surface with a predetermined and constant slope. Such servo spirals may be written on the disk surface with an external media writer before assembly of the disk drive, or with a servo writing machine that uses an external precision actuator to position the disk drive actuator with a mechanical push pin through an opening in the disk drive housing. In either case, setup and use of such external equipment for each individual HDD is time-consuming and expensive in the context of high-volume manufacturing.
In light of this, in-drive spiral-writing schemes have been employed, in which an HDD writes servo spirals itself prior to performing the SSW process. High quality servo spirals are evenly spaced circumferentially from each other, and when servo spirals are self-written by the HDD, the accuracy of such circumferential spacing can be strongly dependent on an accurately implemented launch point when the HDD begins writing each servo spiral. Accurate launch points for writing servo spirals can be achieved by precisely timed initiation of servo spiral writing. However, schemes that rely on precise timing for launching servo spirals correctly can be problematic to implement and/or require specialized hardware. Accordingly, there is a need in the art for a method of generating accurate servo spirals on a disk surface of an HDD without the use of external equipment.